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This invention relates in general to an electromagnetic suspension and
guide system for a magnetically suspended vehicle, and more particularly
to a control system for controlling the electromagnetic suspending and
guiding operations of such vehicle.
In the past, there has been known an electromagnetic suspension and guide
system for a magnetically suspended vehicle wherein the vehicle is
provided with an electromagnet for suspending the vehicle and a separate
electromagnet for guiding the vehicle, these electromagnets being secured
to the vehicle in such a manner that they are positioned to face an
armature rail of ferromagnetic material laid on the ground, energizing
currents supplied to these electromagnets are controlled so that the
vehicle is kept magnetically suspended or floated and at the same time
guided in the lateral direction with respect to the armature rail, and the
vehicle thus suspended or floated and guided is moved along the armature
rail by a propelling force such as given by a linear motor being secured
to the vehicle. However, in such known system, it is naturally inevitable
that the overall weight of the magnetically suspended vehicle becomes too
heavy due to the necessity of using a separate electromagnet for guiding
the vehicle in addition to an electromagnet for floating the same.
Also, as disclosed in the Official Gazette for Japanese Patent Application
Public Disclosure No. 16323/1973, there has been proposed an
electromagnetic suspension and guide system which employs a plurality of
electromagnets secured to the vehicle and disposed in zigzag or
alternately staggered fashion with respect to an armature rail of
inverted-U shape in cross section in an attempt to eliminate the need of
additional guide electromagnet.
However, this known system has the drawback that there occurs eddy currents
in the armature rail due to the fact that the direction in which the
magnetic fluxes generated by the electromagnets intersect the opposing
armature rail may change alternatively as the vehicle is moved along the
rail, thus applying an increased magnetic drag force to the vehicle, and
furthermore, there is the problem that there occur yawing and pitching
moments about the center point between the electromagnets disposed in
zigzag fashion during running of the vehicle.
Moreover, there has been disclosed another system in the Official Gazette
for Japanese Patent Application Public Disclosure No. 16322/1973 wherein
the vehicle is provided with an electromagnet core of inverted-T shape in
cross section which is disposed in the groove of an armature rail of
inverted-U shape in cross section in an attempt to have electromagnets for
suspending and guiding purposes integrated as a unit.
However, this known system has the disadvantage that because the upper part
of the electromagnet core comes deeply into the inside of the armature
rail groove, there is naturally a substantial restriction on the
movability or allowance in lateral movement of the electromagnet core,
and, particularly when an electromagnet core of a relatively long
dimension is used, it is impossible to make the curvature of the armature
rail large in an area where the rail is to be curved, since the distance
or gap between the electromagnet core and the armature rail will become
unduly small or the core would even contact with the rail. Furthermore,
this known system has the disadvantage that when an uncontrolled constant
energizing current is supplied to the windings of the guide magnet, or
when control is made only in the vertical direction by the suspension
magnet, there is produced no such automatic restoring force as to restore
and keep the electromagnet core at its neutral lateral position, and,
further, unless lateral control of the electromagnet core is positively
made at all times, the lateral stability of the electromagnet core would
be lost and the core would be deflected undesirably toward either lateral
direction. In addition, this known system has the disadvantage that unless
particular means are provided to assure the lateral stability of the
vehicle at a switch area where the armature rail diverge or converge, the
ability of the system to make lateral control of the vehicle would be
lost.
In consideration of such defects and disadvantages of the prior arts as
mentioned above, it would be advantageous if any improvement can be made
available to overcome and obviate such defects.
Therefore, it is a primary object of the invention to provide an improved
electromagnetic suspension and guide control system for magnetically
suspended vehicles which incorporates an integrally constructed
electromagnet adaptable for both suspension control and lateral guide
control purposes.
It is another object of the invention to provide an improved
electromagnetic suspension and guide control system which requires a
relatively small number of components, thus affording a relatively light
overall weight of such vehicle.
It is still another object of the invention to provide an improved
electromagnetic suspension and guide control system which exerts only a
relatively smaller magnetic drag force to the vehicle and produces
substantially no yawing moment in the vehicle even when it is controlled
in the lateral direction during running thereof along an armature rail.
It is a further object of the invention to provide an improved
electromagnetic suspension and guide control system wherein the
electromagnet secured to the vehicle can be moved over a relatively wide
range in the lateral or transverse direction.
It is a still further object of the invention to provide an improved
electromagnetic suspension and guide control system wherein the
magnetically suspended vehicle has an automatic restoring force in the
lateral direction despite the fact that the vehicle is controlled only in
the vertical direction.
It is a further object of the invention to provide an improved
electromagnetic suspension and guide control system which consumes a
relatively small quantity of electric power during operation.
These object are attained, in accordance with the invention, by an improved
electromagnetic suspension and guide control system wherein an elongated
armature rail fixedly mounted along a track along which a magnetically
suspended vehicle is to travel and an electromagnet core secured to the
vehicle and disposed in an opposing relationship to said armature rail are
both designed to have a three-legged shape in cross section but different
widths from each other, and at least the side legs of the electromagnet
core are provided with control windings wound thereon, respectively, so
that the guiding of the vehicle in lateral direction as well as the
vertical gap between the electromagnet core and the armature rail can be
controlled by controlling the energizing currents supplied to the windings
wound on the legs of the electromagnet core. Since the electromagnet core
and the opposing armature rail have different widths, there is produced a
lateral component in the electromagnetic force developed between the legs
of the electromagnet core of the vehicle and the legs of the armature rail
when the windings of the electromagnet are energized. As examples of
extreme cases, when the number of lines of magnetic flux passing through
the right side leg of the electromagnet core is maximum and the number of
lines of magnetic flux passing through the left side leg thereof is
minimum, the force applied to the electromagnet core is such that the
right side leg of the electromagnet core comes closest to the right side
leg of the armature rail. On the contrary, when the number of lines of
magnetic flux passing through the left side leg of the electromagnet core
is maximum and the number of lines of magnetic flux passing through the
right side leg thereof is minimum, the force applied to the electromagnet
core is such that the left side leg of the electromagnet core comes
closest to the left side leg of the armature rail. In all cases, the
controlling of the number of lines of magnetic flux passing through the
right and left side legs of the electromagnet core is made in such a
manner that the overall upward force applied to the vehicle is kept
substantially unchanged in order to keep the vehicle suspended at a
preselected height. Thus, the electromagnet secured to the vehicle can
perform the function of controlling the guiding of the vehicle in the
lateral direction, in addition to its ordinary function of controlling the
gap between the electromagnet core and the armature rail.
In another embodiment of the invention, the central leg of the
electromagnet core is also provided with windings wound thereon for
controlling chiefly the upward suspending or lifting force applied to the
electromagnet core and hence to the vehicle which secures the core.
Means are provided for controlling the energizing currents supplied to the
windings of the electromagnet. Such current controlling means may include
a gap detector for determining the distance between the armature rail and
the electromagnet core and/or another gap detector for determining the
lateral position of the electromagnet core relative to the armature rail,
and electrical circuit means for determining the magnitude of currents to
be supplied to the windings of the electromagnet.
The nature, principle, and details of the present invention as well as
further objects and advantages thereof will become more apparent from the
following detailed description with respect to preferred embodiments of
the invention when read in conjunction with the accompanying drawings, in
which like parts are designated with like reference numerals.
In the drawings,
FIG. 1 is a vertical cross-sectional view showing the case where the
invention is applied to a magnetically suspended vehicle having two rows
of electromagnet cores secured thereto near its lower end portions and
allowed to travel along a track having two opposing rows of armature
rails;
FIG. 2(a) is a schematic diagram showing a preferred embodiment of the
invention, and FIG. 2(b) shows one example of the electrical control
circuit used in the arrangement of FIG. 2(a);
FIG. 3(a) through (c) are diagrammatic views illustrating how the control
operation can be effected in the lateral direction of the electromagnet
core shown in FIG. 2(a) in accordance with the invention;
FIG. 4 is a schematic diagram showing another embodiment of the invention;
FIG. 5 is a diagrammatic view, in vertical section, showing how the
invention can be applied to a suspended type of vehicle;
FIG. 6(a) is a view illustrating the arrangement of the armature rail
according to the invention in a switching area thereof;
FIG. 6(b) is a vertical cross-sectional view taken along line A-A' of FIG.
6(a);
FIG. 7(a) is a view illustrating the arrangement of an exemplary armature
rail according to a prior art in a switching area thereof;
FIG. 7(b) is a vertical cross-sectional view taken along line B-B' of FIG.
7(a);
FIG. 8(a) is a diagrammatic cross-sectional view illustrating a mode of
using of a part of the armature rail according to the invention as a
mechanical brake for the vehicle; and
FIG. 8(b) and (c) are diagrammatic cross-sectional views illustrating modes
of using of prior art armature rails as mechanical brakes, respectively.
In the accompanying drawings, there are shown, for illustrative purposes
only but not in any way for limitations, preferred embodiments of the
improved electromagnetic suspension and guide control system according to
this invention.
Description will now be given as to the typical preferred embodiments of
the invention in conjunction with the accompanying drawings.
Referring to FIG. 1, a pair of electromagnet cores 3 each having a
three-legged shape in cross section and fixedly mounted on a magnetically
suspended vehicle 2 are positioned to face a pair of armature rails 1 of
ferro-magnetic material laid on the ground by means of a rail support (not
numbered) with a preselected gap "d" therebetween. Although the drawing
shows only one electromagnet core on each side of the rail support, it is
to be noted that the vehicle 2 may be provided with a plurality of such
electromagnet cores along the length thereof. The electromagnet core 3 has
side legs 4, 5 and a central leg 6 while the armature rail 1 has side legs
7, 8 and a central leg 9, as shown.
According to the invention, the width of the electromagnet core 3 is made
smaller or greater than that of the armature rail 1 (FIG. 1 shows, by way
of example, an electromagnet core 3 having a smaller width than that of
the armature rail 1), and the central leg 6 of the core 3 is positioned to
face the central leg 9 of the armature rail 1. There are wound windings on
side legs 4, 5 of the core 3, as described later in conjunction with FIG.
2, and there is also wound a winding on the central leg 6 thereof as will
be further described in connection with FIG. 4. When energizing currents
are supplied to these windings, magnetic fluxes are produced which pass
through a magnetic circuit comprising the armature rail 1. By controlling
the magnitude of the energizing currents supplied to the electromagnet
core windings, the electromagnetic attractive force between the
electromagnet core 3 and the rail 1 can be adjusted to control the
suspending and lateral guiding of the vehicle. The vehicle 2 thus
electromagnetically suspended may be driven longitudinally along the
armature rail by a separate propelling means such as linear motor
arrangement 24. Because the essence of the invention is concerned with how
to control the suspending or lifting and lateral guiding of the vehicle,
and not with how to propel it along the length of the rail, such
propelling means will not be explained in detail.
FIG. 2(a) is a schematic diagram of one example of the electromagnetic
suspension and guide control system according to the invention wherein the
electromagnet core 3 has a smaller width than that of the armature rail 1
and is provided with windings wound only on its side legs, showing that
the core 3 is in its neutral position and is located to face the armature
rail 1 with a given gap "d" therebetween. FIG. 2(b) shows one example of
an electric control circuit which can be used in the arrangement of FIG.
2(a). FIG. 3(a) through (c) diagrammatically illustrate how a lateral
control force is exerted on the electromagnet core 3 by changing the state
of energization of the windings wound on the side legs of the core 3.
In the arrangement shown in FIG. 2(a), in order to maintain a preselected
width "d" of the gap between the electromagnet core 3 and the armature
rail 1, a vertical gap detector 10 having a fixed relationship to the core
3 produces an electrical signal corresponding to a vertical deviation of
the core 3 from the armature rail 1 and supplies it to an operational
amplifier circuit 22. The output signal from the operational amplifier
circuit 22 is applied to respective current controllers 11, 12 which
provide energizing currents to the windings 14 and 15 on the side legs of
the core 3, respectively.
With the arrangement shown in FIG. 2(a), even if control is effected only
in the vertical direction, there is produced an automatic restoring force
which tends to restore the electromagnet core 3 to its neutral position in
case the core has been deflected in either lateral direction, because, in
such case, the direction of the flux .PHI.c passing through the central
leg 6 of the core 3 is tilted relative to the vertical and because the
horizontal components F1g., F2g of the forces F1, F2 developed
respectively by the magnetic fluxes .PHI.1, .PHI.2 passing through the
left and right side legs 4, 5 of the core 3 vary. But, in order to provide
a positive lateral control effect on the core 3 in addition to this
automatic restoring effect, there is provided a second gap detector 13
having a fixed relationship to the core 3 and adaped to detect the lateral
position of the electromagnet core 3 with respect to the armature rail 1.
The gap detector 13 produces an electrical signal corresponding to a
lateral deviation of the core 3 relative to the armature rail 1 and
applies it to an operational amplifier circuit 23, the output signal from
which is applied to the current controllers 11, 12, thus changing the
energizing currents supplied to the windings 14, 15 wound on the side legs
of the core 3. Thus, the energizing current obtained in accordance with
the lateral deviation of the core 3 relative to the armature rail 1 is
superposed on the energizing current obtained in accordance with the
vertical deviation of the core 3 from the rail 1 and the resultant signal
is supplied to the windings 14, 15 to control both the suspending and
lateral guiding of the core 3 secured to vehicle.
In this manner, supposing that there is no external force applied to the
core 3 and there is no disturbing factor such as the abnormality in shape
of the rail portion, the arrangement shown in FIG. 2(a) assures that the
core 3, and hence the vehicle securing it, is kept at its neutral position
with a predetermined vertical distance "d" and with a preselected
horizontal distance "l" measured between the detector 13 and the armature
rail 1, giving the relationship that F1l equals F2l in magnitude and has
the same sense as that of F2l while F1g equals F2g in magnitude but has an
opposite sense from that of F2g, as shown in FIG. 2(a) where F1l and F1g
represent the vertical and horizontal components of the force F1 developed
by the magnetic flux .PHI.1, respectively, and F2l and F2g represent the
vertical and horizontal components of the force F2 developed by the
magnetic flux .PHI.2, respectively. In the central leg 6 of the core 3
there exists an upwardly directed attractive force Fc developed by the
magnetic flux .PHI.c.
FIG. 2(b) shows one example of an electrical control circuit which may be
used in the arrangement of FIG. 2(a). Firstly, description will be given
as to the vertical gap control operation. An electrical signal from the
detector 10 is subtractively combined with a reference signal from a gap
setting device 1a, and the resultant difference signal is applied to a
linear amplifier circuit 2a and a differential amplifier circuit 3a.
Output signals from the amplifier circuits 2a, 3a are additively combined
and the combined signal is applied to the current controllers 11, 12 to
provide currents of the same magnitude in the windings 14, 15 on the side
legs 14, 15 of the core 3. On the other hand, in order to effect guide
control of the core 3 in the lateral direction, a difference signal
between a signal from the detector 13 and that from a gap setting device
4a is applied to a linear amplifier circuit 5a and a differential
amplifier circuit 6a. Output signals from the amplifier circuits 5a, 6a
are additively combined and the combined signal is applied with negative
sign to the current controller 11 and with positive sign to the current
controller 12, and as a consequence, the current in one of the side leg
windings of the core 3 is increased while the current in the other winding
thereof is decreased.
A block designated by 7a and drawn in a phantom line in FIG. 2(b) shows an
element for providing a signal which permits the system to take into
account special factors to improve the stability thereof, such factors
including the differentiation of second order of the signal representing
the gap between the core 3 and the rail 1 or the gap between the detector
13 and the rail 1, the magnitude of the magnetic flux, the magnitude of
energizing currents, the acceleration of the core 3, etc.
In the arrangement of FIG. 3(a) through (c), for clarification and
simplification purposes, the electromagnet core 3 is shown assuming, as
the intended position, its neutral position with respect to the armature
rail. With the electromagnet core 3 in such intended position, a lateral
control force will be actually produced in the following cases: i.e., (1)
when an electrical signal is given to the gap setting device 1a or 4a, (2)
when the core 3 has a velocity or acceleration component in the lateral
direction, and (3) when the core 3 is deflected laterally by only a slight
distance from its neutral position, but the linear amplifier circuits 2a,
5a have so high a gain as to sense even such a slight deflection, to vary
the magnitude of input signals to the controllers 11, 12.
FIG. 3(a) shows such a condition of the electromagnet that there is a
relatively large current flowing through the winding on the right side leg
5 of the core 3, while there exists substantially no current flowing
through the winding on the left side leg 4 thereof. In FIG. 3(a), the
lines of magnetic flux generated in the right side leg 5 define magnetic
circuits respectively passing through the central legs 6, 9 and the left
side legs 4, 7, then returning into the right side leg 5, in which
condition a rightward control force having the magnitude of F2g-F1g is
exerted on the electromagnet core 3. In order to make this control force
further effective, an electric current may be permitted to flow in the
winding on the left side leg 4 so that lines of magnetic flux of opposite
sense as shown by broken lines in FIG. 3(b) are generated for cancelling
the magnetic flux generated by the winding on the right side leg 5 of the
core 3 and passing through the left side legs 4, 7 as shown in FIG. 3(a).
Thus, the magnetic flux circuit of FIG. 3(b) may be superposed upon that
of FIG. 3(a). The result of such superposition is shown in FIG. 3(c) in
which it is seen that a stronger lateral control of the core 3 is effected
by the force F2G.
In performing the lateral control of the core 3 with respect to the
armature rail in this way, the lines of magnetic flux may be concentrated
in one of the side legs of the core 3 with the result that there may be
produced a rolling moment on the core 3 about an axis perpendicular to the
plane of paper, but this problem may be solved by providing a row of
electromagnets on each of the left and right sides of the vehicle (FIG. 1
shows such a case, although only one electromagnet core 3 on each side of
the vehicle 2 can be seen therein), or by constituting the vehicle in a
suspended form (as will be later described in conjunction with FIG. 5).
Although description has been given as to the case where there occurs a
control force working in the right hand direction in conjunction with FIG.
3(a) through (c), the same description can also be applied to the case
where such control force works in the left hand direction.
Also, with the arrangement according to the invention, even if the
electromagnet core 3 has, as its intended position, a deflected position
away from its neutral position, it is likewise possible to generate a
control force in any desired lateral direction in addition to the
afore-said automatic restoring force by the control of the energizing
current supplied to the electromagnet windings, whereby it is possible to
maintain the electromagnet core 3 at a desired position against an
external force, or to deflect intentionally the core in any lateral
direction, such features in operation being useful particularly in the
switching operation of the vehicle, as will be further described
hereinafter, and furthermore, it is possible to provide a dumping effect
by applying an energizing current to the electromagnet windings so as to
produce a control force which acts in the opposite direction to the
lateral movement of the electromagnet which has a magnitude proportional
to the lateral deflecting velocity of the electromagnet. Such lateral
control function cannot be made available from the construction of an
electromagnet wherein the width of the electromagnet core and that of the
opposing armature rail are the same with each other, because it would be
impossible for such construction of an electromagnet to provide an extra
lateral control force other than the automatic restoring force which is
generated when the electromagnet core is deflected away from its central
position.
Although the above description given in conjunction with FIGS. 2 and 3(a)
through (c) have been confined to an embodiment of the invention wherein
the width of the electromagnet core is smaller than that of the armature
rail, the operation and the technical effect produced by the construction
of an electromagnet wherein the width of the electromagnet core is greater
than that of the armature rail do not differ from those of the above said
embodiment, excepting that the control of energizing currents in the side
legs thereof is effected in an opposite manner. The greater the difference
in width between the electromagnet core and the armature rail is, the
greater the lateral control force becomes, but the more the electric power
is required.
FIG. 4 shows another embodiment of the invention wherein there is provided
an independent winding 16 on the central leg 6 of the electromagnet core 3
for controlling the vertical lifting attractive force applied to the
vehicle and wherein the windings 14, 15 on the side legs of the core 3 are
connected in series to each other for controlling the lateral force
applied to the vehicle. The function and effect obtainable from the
arrangement shown in FIG. 4 are similar to those obtainable from the
arrangement shown in FIGS. 2 and 3(a) through (c). In the arrangement of
FIG. 4, there is produced a lateral control force which corresponds to the
direction and magnitude of the current flowing through the windings 14, 15
on the side legs of the electromagnet core 3. In FIG. 4, there are shown
current controllers designated by 17 and 18 which have a similar function
to the current controllers 11, 12 shown in FIG. 2.
FIG. 5 is a diagrammatic view, in vertical cross-section, showing the case
where the invention has been applied to a suspended type of vehicle. In
this arrangement, an electromagnet core 3 having a three-legged shape in
cross section fixedly mounted on the upper side of a vehicle 2 is disposed
in an opposing relationship to an armature rail 1 suspended from a support
20 erected on the ground, so that the vehicle 2 is caused to be
electromagnetically suspended by the magnetic attractive force exerted on
the core 3. There are provided protector devices 19 adapted to prevent the
vehicle 2 from dropping down due to loss or lack of the suspending
magnetic force during running of the vehicle 2.
FIG. 6(a) shows diagrammatically the arrangement of the armature rail in a
switching area thereof for the suspended type of vehicle shown in FIG. 5,
and FIG. 6(b) is a cross-sectional view taken along line A-A' in FIG.
6(a). FIG. 7(a) is a diagrammatic view similar to FIG. 6(a) showing a
prior art armature rail as disclosed in Japanese Patent Application Public
Disclosure No. 16322/1973 as referred to hereinbefore, and FIG. 7(b) is a
cross sectional view taken along line B-B' in FIG. 7(a).
According to the construction of the armature rail according to this
invention as shown in FIG. 6(a) and (b), it is possible to carry out the
switching of the vehicle 2 in any desired branching direction through
electrical control without the necessity of any particular switching means
at the switching area. More particularly, when it is desired to switch the
vehicle in the switching area to, for instance, the right branch rail as
viewed in FIG. 6(a), it is only required to increase the magnetic flux
density in the right side leg of the electromagnet core and at the same
time temporarily put down the left side protector device 19 toward the
left side before entry of the vehicle in the switching area. During such
switching operation, the protective function of the left side protector
device 19 is temporarily lost, but there is no danger of the vehicle
falling down, because the right side protector device 19 is still
effective in function. In contrast, in the prior art construction of
electromagnet as shown in FIG. 7(a) and (b), it is impossible to switch
the vehicle to any described branching direction without the provision of
switching means.
More particularly, as seen from the rail arrangement shown in broken lines
in FIG. 7(a), it is inevitably necessary to take off a relatively long
part of the right side leg portion of the armature rail for
straightforward travel of the vehicle, or to take off a relatively long
part of the left side leg portion of the rail for a right turn of the
vehicle, and, consequently, a lateral control force to be applied to the
vehicle is lost during its passage through the switching area, and thus
the electromagnet core with an inverted-T shape in cross section would
come into contact with either one of the wall portions of the armature
rail.
FIG. 8(a) shows an aspect of use as a mechanical brake of the armature rail
according to the present invention. FIG. 8(b) and (c) show aspects of use
as mechanical brakes of the armature rails having different cross
sectional shapes from that of the invention, respectively. In FIG. 8(a)
through (c), reference numeral "21" designates a brake element fixedly
mounted on the electromagnet and the arrows indicate the areas of the rail
against which brake shoes are pressed. For a magnetically suspended
vehicle, such a mechanical brake mechanism is very important. The braking
device as shown in FIG. 8(a) which is adapted to exert a braking force on
both sides of the central leg portion of the armature rail is more
advantageous in comparison with the other two types shown in FIG. 8(b) and
(c): the braking device shown in FIG. 8(b) has the disadvantage that there
might occur harmful vibrations due to deformation of the armature rail,
while the braking device shown in FIG. 8(c) has the disadvantage that an
eccentric moment of force might be produced in the electromagnet core
during braking operation.
From the foregoing, it will be seen that according to this invention, there
is provided effective control of a magnetically suspended or floated
vehicle by using a single integrally constructed electromagnet for both
suspending and lateral guiding operations, and that highly reliable
suspending and guiding control can be achieved from the construction of a
control system incorporating a relatively few components. Furthermore, in
the arrangement according to the invention, the direction in which the
magnetic fluxes generated by the electromagnet windings intersect the
armature rail is substantially constant, and this is particularly useful
when the vehicle is provided with a plurality of electromagnets disposed
in a closely spaced relationship to one another along the length of the
armature rail, because it reduces eddy currents produced in the armature
rail portion on which the vehicle is running whereby the magnetic drag
force applied to the vehicle is substantially reduced, and further no
yawing moment of force is generated from the lateral control of the
electromagnet core. Also, with the construction of the electromagnet core
and armature rail according to the invention, there is no danger of the
electromagnet core contacting with the armature rail side walls even if
the rail is designed to have a large radius of curvature. Also, in the
system according to the invention, the electromagnet core has an automatic
restoring force even if lateral guiding control is not effected.
Furthermore, the invention provides an advantageous feature in its
application to a switching area of the armature rail, when it is applied
to a suspended type of vehicle, and in addition, the armature rail has
such a construction that a part thereof can be used to advantage as a
mechanical brake for the vehicle.
Having described the foregoing embodiments of the invention, it is now
evident to those skilled in the art that other embodiments incorporating
its concept may be used. Therefore, it is to be understood that the
invention should not be limited to such disclosed embodiments.
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